Every one knows that objects fall because of gravity, even before Newton. Newton did not discover gravity, but discovered that gravity is universal. It is the same force that pulls an apple off a tree, holds the moon in orbit, and that both Earth and the moon are similarly held in orbit around the sun. He also discovered that all objects in the universe attract each other. [1]
All forces of objects are due to interaction. There are four types of fundamental processes responsible for all observe processes are: Strong, electromagnetic, weak and gravitational. Gravitational Interaction is weak, fundamental interaction between two physical objects due to their mass and energy, especially an interaction occurring between elementary particles. All forces of objects are due to interaction. There are four types of fundamental processes responsible for all observe processes are: Strong, electromagnetic, weak and gravitational. Gravitational Interaction is weak, fundamental interaction between two physical objects due to their mass and energy, especially an interaction occurring between elementary particles.
The Gravitational Interaction, some 10^40 times weaker than the electromagnetic interaction, it is the weakest of all. The force that it generates acts between all bodies that have mass and the force is always attractive. The interaction can be visualized in term of a classical field of force in which the strength of force falls off with the square of the distance between the interacting body. The hypothetical gravitational quantum, the graviton, is also useful concept in some contexts. On the atomic scale, the gravitational force is negligibly weak, but on the cosmological scale, where masses are enormous, it is immensely important in holding the components of the universe together. Because Gravitational Interactions are long-ranged, there is well-defined macroscopic theory in general relativity. At present, there is no satisfactory quantum theory of gravitational interaction.
Black Hole: A black hole is an astronomy theoretical celestial object, formed when a massive star collapses from its own gravity. A black hole has such a strong pull of gravity that not even light can escape from it.
Gravitational Interaction: A weak, fundamental interaction between two physical objects due to their mass and energy, especially an interaction occurring between elementary particles.
Fundamental Interactions: Also called fundamental force, they are the way that simplest particle in the universe interact with one another.
Strong Interactions: Interactions that responsible for forces between quarks and gluons and nuclear binding.
Electromagnetic: Interactions that responsible for electric and magnetic forces.
Weak Interactions: Interactions that responsible for the instability of all but the least massive fundamental particles in any class.
Image courtesy of MAGCRAFT advanced magnetic materials
We are familiar with magnetic field by playing with iron filings and magnet. Iron filings trace out a pattern of magnetic field lines in the space surround the magnet. The shape of the force field is revealed by magnetic field lines. Magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole as you can see in the picture on the right.[3]
Similar to magnetic field, the gravitational field is the kind of force the surround massive objects. Like the iron filings around the magnet,g Earth's gravitational field can be represented by imaginary field lines. The field lines are closer together where the gravitational field is stronger, Farther away, where the field lines are farther apart, the field is weaker. Arrows show the field direction, and the direction of the field at any point is along the line the point lies on. Any mass in the vicinity of Earth will be accelerated in the direction of the field line at that location. The picture below the magnetic field shows the Earth magnetic field lines. We know there is an acceleration due to gravity of about 9.8 m/s^2 down at every point in the room. Another way of saying this is that the magnitude of the Earth's gravitational field is 9.8 m/s^2 down at all points in this room. Gravitational field: g = F/m (where F is the force of gravity.) [2]
The numerical value of g (gravity) at Earth's surface depends on the mass of earth and its radius (g=GM/r^2). If Earth had a differe
Picture courtesy of WIKIMEDIA COMMONS gravitational field lines
nt mass or radius, g at its surface would have a different value. We can calculate the acceleration due to gravity at the surface of that planet if we know the mass and radius of any planet. The strength of Earth's gravitational field, like the strength of its force on objects, follows the inverse-square law outside Earth. So g weakens with increasing distance from Earth.
Gravitational Field Inside a Planet
Imagine a hole drill from North Pole through South Pole completely. If you started at the North Pole end, you'd fall and gain speed all the way down to the center, and then overshoot and lose speed all the way to the South Pole. Without air drag, the trip would take nearly 45 minutes. If you failed to grab the edge, you;d fall back toward the center, overshoot, and return to the North Pole in the same amount of time. You'd gain speed moving toward the center, and lose speed moving away from the center. Half way to the center of the planet, g has 1/2 of its surface value, and at the center of the planet g=0 N/Kg.
Picture Courtesy Of "Journey through the center of the Earth"
At the beginning of the fall, the gravitational field strength and your acceleration are g, but you'd find they steadily decrease as you continue toward the center of Earth. You are being pulled "downward" toward Earth's center, you are also being pulled "upward" by the part of Earth that is "above" you. In fact, when you get to the center of Earth, the pull "down" is balanced by the pull "up". You are pulled in every direction equally so the net force on you is zero. There is no acceleration as you whiz with maximum speed past the center of Earth.
Weight and Weightlessness
Weight is a force of gravity acting on a mass. If you were to move an object from Earth to Moon, the mass of the object would not change but it will be weightless. The amount of matter in that object always stay the same, but the gravitational force action on the object by the Moon would be less than the gravitational force acting on the object by the Earth. Weight should be measure in Newton and has a direction component. The direction is normally downward due to gravity, a force between two objects that depends on the mass of the objects and the distance between them. The Earth has much larger mass than the Moon. A component of weight can also be sideways, such as the force of a car hitting a wall. The weight of an object is w = mg, where m is the mass of the object, and g is the acceleration of free fall.
The phenomenon of "weightlessness" occurs when there is no force of support on your body. When your body is effectively in "free fall", accelerating downward at the acceleration of gravity, then you are not being supported. The sensation of apparent weight comes from the support that you feel from the floor, from a chair, etc. Different sensations of apparent weight can occur on an elevator since it is capable of zero or constant speed (zero acceleration) and can accelerate either upward or downward. If the elevator cable breaks then both you and the elevator are in free fall. The resultant experience of weightlessness might be exhilarating if it weren't for the anticipation of the quick stop at the bottom.[6]
If you are standing on a scale in a moving elevator, you would find your weight reading would change —not when you are at the steady motion but during accelerated motion. The scale would show an increase of your weight when the elevator accelerate upward, and decrease as it accelerate downward. If the elevator cable broke and the elevator fell freely, the scale reading would register zero; at this point you will feel weightless, because your insides would no longer be supported by your legs and pelvic region. The picture on the right show the weight and weightlessness in an elevator.[8]
Black Hole
A Black Hole is an compact object that its gravitational force is strong enough to prevent light or anything else from escaping. The existence of Black Holes was first propose in the 18th century, based on the known law of gravity. The more massive of an object, or the smaller its size, the larger gravitational force felt on its surface.[7]
Black holes obey all laws of physics, including the laws of gravity. Their remarkable properties are in fact a direct consequence of gravity.
In 1687, Isaac Newton showed that all objects in the Universe attract each other through gravity. Gravity is actually one of the weakest forces known to physics. In our daily life, other forces from electricity, magnetism, or pressure often exert a stronger influence. However, gravity shapes our Universe because it makes itself felt over large distances. For example, Newton showed that his laws of gravity can explain the observed motions of the moons and planets in the Solar System.
refined our knowledge of gravity through his theory of general relativity. He first showed, based on the fact that light moves at a fixed speed (671 million miles per hour), that space and time must be connected. Then in 1915, he showed that massive objects distort the four-dimensional space-time continuum, and that it is this distortion that we perceive as gravity. Einstein's predictions have now been tested and verified through many different experiments. For relatively weak gravitational fields, such as those here on Earth, the predictions of Einstein's and Newton's theories are nearly identical. But for very strong gravitational fields, such as those encountered near black holes, Einstein's theory predicts many fascinating new phenomena.[9]
Here is a short video clips that shows Black Holes, Neutron Stars, Space and Time.[10]
Gravitational Interaction
Every one knows that objects fall because of gravity, even before Newton. Newton did not discover gravity, but discovered that gravity is universal. It is the same force that pulls an apple off a tree, holds the moon in orbit, and that both Earth and the moon are similarly held in orbit around the sun. He also discovered that all objects in the universe attract each other. [1]
All forces of objects are due to interaction. There are four types of fundamental processes responsible for all observe processes are: Strong, electromagnetic, weak and gravitational. Gravitational Interaction is weak, fundamental interaction between two physical objects due to their mass and energy, especially an interaction occurring between elementary particles. All forces of objects are due to interaction. There are four types of fundamental processes responsible for all observe processes are: Strong, electromagnetic, weak and gravitational. Gravitational Interaction is weak, fundamental interaction between two physical objects due to their mass and energy, especially an interaction occurring between elementary particles.
The Gravitational Interaction, some 10^40 times weaker than the electromagnetic interaction, it is the weakest of all. The force that it generates acts between all bodies that have mass and the force is always attractive. The interaction can be visualized in term of a classical field of force in which the strength of force falls off with the square of the distance between the interacting body. The hypothetical gravitational quantum, the graviton, is also useful concept in some contexts. On the atomic scale, the gravitational force is negligibly weak, but on the cosmological scale, where masses are enormous, it is immensely important in holding the components of the universe together. Because Gravitational Interactions are long-ranged, there is well-defined macroscopic theory in general relativity. At present, there is no satisfactory quantum theory of gravitational interaction.
Vocabulary
Gravitational Fields
We are familiar with magnetic field by playing with iron filings and magnet. Iron filings trace out a pattern of magnetic field lines in the space surround the magnet. The shape of the force field is revealed by magnetic field lines. Magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole as you can see in the picture on the right.[3]
Similar to magnetic field, the gravitational field is the kind of force the surround massive objects. Like the iron filings around the magnet,g Earth's gravitational field can be represented by imaginary field lines. The field lines are closer together where the gravitational field is stronger, Farther away, where the field lines are farther apart, the field is weaker. Arrows show the field direction, and the direction of the field at any point is along the line the point lies on. Any mass in the vicinity of Earth will be accelerated in the direction of the field line at that location. The picture below the magnetic field shows the Earth magnetic field lines. We know there is an acceleration due to gravity of about 9.8 m/s^2 down at every point in the room. Another way of saying this is that the magnitude of the Earth's gravitational field is 9.8 m/s^2 down at all points in this room. Gravitational field: g = F/m (where F is the force of gravity.) [2]
The numerical value of g (gravity) at Earth's surface depends on the mass of earth and its radius (g=GM/r^2). If Earth had a differe
Gravitational Field Inside a Planet
Imagine a hole drill from North Pole through South Pole completely. If you started at the North Pole end, you'd fall and gain speed all the way down to the center, and then overshoot and lose speed all the way to the South Pole. Without air drag, the trip would take nearly 45 minutes. If you failed to grab the edge, you;d fall back toward the center, overshoot, and return to the North Pole in the same amount of time. You'd gain speed moving toward the center, and lose speed moving away from the center. Half way to the center of the planet, g has 1/2 of its surface value, and at the center of the planet g=0 N/Kg .
At the beginning of the fall, the gravitational field strength and your acceleration are g, but you'd find they steadily decrease as you continue toward the center of Earth. You are being pulled "downward" toward Earth's center, you are also being pulled "upward" by the part of Earth that is "above" you. In fact, when you get to the center of Earth, the pull "down" is balanced by the pull "up". You are pulled in every direction equally so the net force on you is zero. There is no acceleration as you whiz with maximum speed past the center of Earth.
Weight and Weightlessness
Weight is a force of gravity acting on a mass. If you were to move an object from Earth to Moon, the mass of the object would not change but it will be weightless. The amount of matter in that object always stay the same, but the gravitational force action on the object by the Moon would be less than the gravitational force acting on the object by the Earth. Weight should be measure in Newton and has a direction component. The direction is normally downward due to gravity, a force between two objects that depends on the mass of the objects and the distance between them. The Earth has much larger mass than the Moon. A component of weight can also be sideways, such as the force of a car hitting a wall. The weight of an object is w = mg, where m is the mass of the object, and g is the acceleration of free fall.
The phenomenon of "weightlessness" occurs when there is no force of support on your body. When your body is effectively in "free fall", accelerating downward at the acceleration of gravity, then you are not being supported. The sensation of apparent weight comes from the support that you feel from the floor, from a chair, etc. Different sensations of apparent weight can occur on an elevator since it is capable of zero or constant speed (zero acceleration) and can accelerate either upward or downward. If the elevator cable breaks then both you and the elevator are in free fall. The resultant experience of weightlessness might be exhilarating if it weren't for the anticipation of the quick stop at the bottom.[6]
If you are standing on a scale in a moving elevator, you would find your weight reading would change —not when you are at the steady motion but during accelerated motion. The scale would show an increase of your weight when the elevator accelerate upward, and decrease as it accelerate downward. If the elevator cable broke and the elevator fell freely, the scale reading would register zero; at this point you will feel weightless, because your insides would no longer be supported by your legs and pelvic region. The picture on the right show the weight and weightlessness in an elevator.[8]
Black Hole
A Black Hole is an compact object that its gravitational force is strong enough to prevent light or anything else from escaping. The existence of Black Holes was first propose in the 18th century, based on the known law of gravity. The more massive of an object, or the smaller its size, the larger gravitational force felt on its surface.[7]
Black holes obey all laws of physics, including the laws of gravity. Their remarkable properties are in fact a direct consequence of gravity.
In 1687, Isaac Newton showed that all objects in the Universe attract each other through gravity. Gravity is actually one of the weakest forces known to physics. In our daily life, other forces from electricity, magnetism, or pressure often exert a stronger influence. However, gravity shapes our Universe because it makes itself felt over large distances. For example, Newton showed that his laws of gravity can explain the observed motions of the moons and planets in the Solar System.
Albert Einstein
Table of Contents
refined our knowledge of gravity through his theory of general relativity. He first showed, based on the fact that light moves at a fixed speed (671 million miles per hour), that space and time must be connected. Then in 1915, he showed that massive objects distort the four-dimensional space-time continuum, and that it is this distortion that we perceive as gravity. Einstein's predictions have now been tested and verified through many different experiments. For relatively weak gravitational fields, such as those here on Earth, the predictions of Einstein's and Newton's theories are nearly identical. But for very strong gravitational fields, such as those encountered near black holes, Einstein's theory predicts many fascinating new phenomena.[9]
Here is a short video clips that shows Black Holes, Neutron Stars, Space and Time.[10]
Presentations
References